To prevent an irradiation beam from being incident to eyes directly or indirectly in case of using a high power light source, various safety measures are taken. For example, when the high power light source is used in a closed space such as a laboratory and a factory, a controlled area in which entrance is limited is provided to secure the safety.
In such a case, it is easy to distinguish the controlled area from the safety area in the closed space. However, in a non-closed space like outdoors, there is a case that it is difficult to set the controlled area. For example, when a long-range communication using a laser beam and a laser ranging are carried out, it is difficult to provide the controlled area between the light source and the irradiation object. Therefore, a technique of securing a safety without providing the controlled area is required even in the situation that the high power light source is used in the non-closed space.
For example, JP 2003-154989A (Patent Literature 1) discloses a laser passage display apparatus having a safeguard by which the irradiation of a laser beam is stopped when a ship invades between a light transmitting buoy and a target buoy. In Patent Literature 1, by detecting an inclination of the light transmitting buoy and the orientation of the target buoy, the target buoy is tracked and the irradiation of the laser beam is stopped in case of the tracking being impossible.
Also, JP H08-29533A (Patent Literature 2) discloses a laser radar that measures a reflected laser beam level and irradiates a laser beam with a safety level for the eyes. The laser radar in Patent Literature 2 calculates a strength level of the laser beam which can be irradiated, according to a distance to an object that is measured by a low power laser beam, and irradiates the laser beam with the calculated strength level. Thus, a long laser ranging becomes possible while securing the safety for a person on a light path.
Moreover, JP 2002-6397A (Patent Literature 3) discloses an image display unit that can prevent that the light projected to a screen is erroneously incident directly to the eyes. In Patent Literature 3, an object in neighborhood of a projection lens is sensed by a photo-coupler and the output of the projection light is controlled according to the sensing of the object. Thus, the display is controlled to a whole black display. Accordingly, it can be prevented that the projection light is incident to the eyes of the human being.
For example, in case of a laser beam of a low energy density, it is enough to secure a safety on a light path. However, in case of a laser beam of a high energy density, there is a case that a reflected laser beam and a scattered laser beam exert harm on persons and electronic circuits. Even in such a case, the safety needs to be secured to the persons in a region except for a region on the light path. In case of using a high power light source, the similar measures need to be performed. However, in the above-mentioned conventional examples, the safety to the human bodies on the light path can be secured but the safety of the objects and the human bodies in a region out of the light path cannot be secured.